Electronic Spectra of Iron-Sulfur Complexes Measured by 2p3d RIXS Spectroscopy

Area of Science:

• Bioinorganic chemistry
• Spectroscopy
• Computational chemistry

Background:

• Iron-sulfur (FeS) proteins are crucial for biological electron transfer and catalysis.
• Understanding their electronic properties, particularly low-energy d-d excited states, is key to deciphering their function.
• Traditional optical spectroscopies have limitations in characterizing these complex electronic transitions.

Purpose of the Study:

• To demonstrate the utility of iron L-edge 2p3d resonant inelastic X-ray scattering (RIXS) for characterizing d-d excited states in FeS complexes.
• To investigate the electronic structure of monomeric, dimeric, and tetrameric FeS model complexes.
• To compare RIXS findings with theoretical predictions.

Main Methods:

• Utilized iron L-edge 2p3d resonant inelastic X-ray scattering (RIXS) spectroscopy.
• Studied a series of monomeric, dimeric [2Fe-2S], and tetrameric [MFe3S4]2+ (M = V, Mo) FeS model complexes.
• Analyzed low-energy electronic excitations (0–10,000 cm−1) and spin-flip transitions.

Main Results:

• RIXS successfully measured d-d excitation spectra across various FeS complexes.
• Revealed a dense manifold of low-lying d-d excited states in dimeric and tetrameric FeS complexes.
• Observed spectral features attributed to covalency and exchange coupling effects.
• Demonstrated RIXS's capability to detect low-energy and spin-flip transitions inaccessible to optical methods.

Conclusions:

• Iron L-edge 2p3d RIXS is a powerful technique for probing the electronic structure of FeS complexes.
• The electronic structure of FeS clusters is more complex than predicted by simplified models, with a greater number of low-lying excited states.
• RIXS results align with and support advanced ab initio theoretical predictions.